1. Field of the Invention
The invention relates generally to magnetoresistive solid-state storage devices, and, more particularly, to minimizing errors in a magnetoresistive solid-state storage device.
2. Related Art
A typical magnetoresistive solid-state storage device, such as a magnetic random access memory (MRAM) device, includes an array of storage cells. Each of the cells is typically constructed of two layers of magnetic film, separated by a dielectric layer. The orientation of the magnetization of one of the layers is alterable, while the orientation of the magnetization of the other layer is fixed or xe2x80x9cpinnedxe2x80x9d in a particular orientation. The magnetic film layer having alterable magnetization is typically referred to as a xe2x80x9cdata storage layerxe2x80x9d and the magnetic film layer which is pinned is typically referred to as a xe2x80x9creference layer.xe2x80x9d
Conductive traces are typically routed across the array of storage cells. These conductive traces are typically arranged in rows and columns. The conductive traces extending along the rows of the storage cells are generally referred to as xe2x80x9cword linesxe2x80x9d and the conductive traces extending along the columns of the storage cells are generally referred to as xe2x80x9cbit lines.xe2x80x9d The word lines and bit lines are typically oriented perpendicular to each other. Located at each intersection of a word line and a bit line, each storage cell stores a bit of information as an orientation of magnetization.
Typically, the orientation of magnetization in the data storage layer aligns along an axis of the data storage layer that is commonly referred to as its easy axis. Typically, external magnetic fields are applied to flip the orientation of magnetization in the data storage layer along its easy axis to either a parallel or anti-parallel orientation with respect to the orientation of magnetization in the reference layer, depending on the desired logic state.
The orientation of magnetization of each storage cell will assume one of two stable orientations at any given time. Typically, these two stable orientations, parallel and anti-parallel, represent the logic values of xe2x80x9c1xe2x80x9d and xe2x80x9c0,xe2x80x9d respectively. Alternatively, a system can be configured to interpret the anti-parallel state as a logic xe2x80x9c1xe2x80x9d and the parallel state as a logic xe2x80x9c0.xe2x80x9d The orientation of magnetization of a selected storage cell may be changed (i.e., from parallel to anti-parallel, or vice versa) by supplying current to a word line and a bit line crossing at the location of the selected storage cell. The currents create magnetic fields that, when combined, can switch the orientation of magnetization of the selected storage cell from parallel to anti-parallel or vice versa.
Ideally, the magnetic fields in each cell of an MRAM array will align in either the parallel or anti-parallel directions. Unfortunately, however, due to imperfections in the magnetic materials used to form MRAM arrays, each cell in the MRAM array may not be a perfect rectangle. Therefore, the magnetic fields in some of the storage cells may be misaligned with respect to each other. The magnetic fields in such a cell will typically demonstrate a preference for aligning in either the anti-parallel orientation or the parallel orientation, which may result in an error when an attempt is made to write data to the cell. In some circumstances, the magnetic fields in a particular cell may even become stuck in either the anti-parallel orientation or the parallel orientation. A cell having a propensity to favor one orientation over the other typically does not switch its orientation reliably when written to, thus introducing an error into the data. For example, assume that it is desired to store the binary number 0000 in an MRAM array. However, when each bit of the binary number 0000 is written to a cell in the array, one of the bits is written to a cell that has a propensity to remain in the orientation of magnetization that corresponds to a logic xe2x80x9c1.xe2x80x9d Therefore, when the number is read from the array, a xe2x80x9c1xe2x80x9d rather than a xe2x80x9c0xe2x80x9d will be read from the cell having a propensity to remain in the orientation that corresponds to a xe2x80x9c1xe2x80x9d (e.g., the number read from the array could be 0010 instead of 0000), thus introducing an error into the system.
Therefore, there is a need for overcoming the deficiencies and inadequacies stated above.
The present disclosure provides exemplar embodiments which allow errors in a magnetoresistive solid-state storage device having a plurality of cells, such as a magnetic go random access memory (MRAM) device array, to be minimized. An illustrative method may be characterized as comprising the steps of identifying cells in a magnetoresistive solid-state storage device which have a failure mode characterized by a propensity to remain in a particular orientation of magnetization, mapping the location of the identified cells, and compensating for the failure mode of a cell at a mapped location.
An illustrative system comprises a testing element configured to identify cells in a magnetoresistive solid-state storage device which have a failure mode characterized by a propensity to remain in a particular orientation of magnetization, a memory element, and a processing element configured to map the location of the identified cells into the memory element and to compensate for the failure mode of a mapped cell.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention, as defined in the appended claims.